The present invention relates to a conductive structure which enables a rotatable roller member to be conducted in the developing unit of an image formation apparatus making use of electrophotography.
Conventionally, an imaging forming apparatus is know, such as a copy machine, a laser beam printer and the like, making use of a so-called electrophotographic image forming method wherein the uniformly charged surface of a photoconductive drum is exposed to light to form a latent image, then charged toner is adhered to the latent image by a developing device to form a toner image, and the toner image is transferred onto a recording sheet and fixed thereon.
In an electrophotographic image forming apparatus as described above, for example, toner accommodated in a developing device is adhered to the photoconductive drum by means of a developing roller. The developing roller, for example, is constructed as follows. A magnet roller having magnetic poles disposed on the outer circumference thereof is rotatably fitted in a cylindrical sleeve composed of a conductive member. The toner is held on the sleeve by the magnetic force of the magnet roller, and a bias voltage. The bias voltage is lower than the voltage of the uniformly charged surface of the photoconductive drum, and higher than that of a latent image formed on the surface of the photoconductive drum by being exposed to light. Thus the toner is charged on the sleeve and transferred onto latent image on the surface of the photoconductive drum.
In the developing device as described above, a structure for applying voltage to the rotating sleeve is constructed such that a contact member having elasticity is urgingly pressed and abutted against the rotary shaft of the sleeve in the radial direction thereof.
With the above arrangement, however, contact failure may occur due to fatigue or deformation of the contact member, or adhered dust and the like, which affects the developing operation, and may result in a poor image formation.
Note that when an abutting force of the contact member is increased to improve the conductivity thereof, a rotating resistance between the contact member and the shaft of the sleeve is increased, which requires an increased rotating drive force, thereby increasing manufacturing cost.